Current Rails In Tube Stations

[Deleted]

Hi Everyone,
I've noticed from a very small age that the current rails in tube stations seem to be a completely different profile to the running rails looking more like square box sections than rails. Is their some logic behind this.
Darren

[Colin]

They are slightly wider as the collection shoe's slide along the top of the current rails. The bogies that they are attached to have a certain tolerance for sideways movement, so the extra width ensures that the collection shoe's maintain contact.

[Deleted]

Thanks Colin. Does this mean the profile is maintained in the tunnels as well as the stations, and why does this not apply to sub surface stock? The current rails are not as tall as the running rails. Can this have something to do with proximity of the current rails to the tunnel sides perhaps.
Darren.

[Colin]

cabdarren said:

Does this mean the profile is maintained in the tunnels as well as the stations

It is indeed.

cabdarren said:

and why does this not apply to sub surface stock?

Could you expand on what you mean by this question?

cabdarren said:

The current rails are not as tall as the running rails. Can this have something to do with proximity of the current rails to the tunnel sides perhaps.

Actually the current rails are above the level of the running rails - they have to be otherwise the collection shoes would foul the running lines as the train goes over points etc.

The proximity to tunnel walls is countered by using two current rails - insulated on porcelain pots and charged at +420 volts & -210 volts in relation to earth. There is more on this HERE.

[Chris M]

Tubeprune's website has a page with a good explantion for some of your queries about this - www.trainweb.org/tubeprune/tractioncurr.htm

[mandgc]

Current rails in Tube tunnels are, or were, of (roughly) square section while on outdoor sections and all Surface lines 'flat bottom' current rails were used.

In some Depot sidings old Bull-head ( chaired) rails were used as current rails needing specially designed chairsto support them.

[Deleted]

Clarification on what i mean.
I've never seen the square type cross-section current rails used on sub-surface lines i.e Circle, and i was refering to the profile of the current rail being physically shorter in height than the profile of a running rail. Sorry for any confusion. I had a look at Tubeprunes website but still no explanation why the different profiles are used
Darren.

[Colin]

I think I know what you are getting at ;D

In the past LUL has always used [current] rails which are larger looking than the running rails - as found on NR third rail lines. Recently they have started fitting a lighter weight aluminum version, most notably on the JLE. Assuming this is what you mean, yes it is smaller; I suspect that the design of it (being more rounded on top) means the chances of the collection shoe losing contact is mitigated. In any case, the end result will be that the current rails will always be at the same height regardless of which type is actually fitted (though to complicate matters, the outside positive rail is always higher than the centre negative rail).

Are we getting closer? ;D

[Deleted]

We are difinately getting closer This is what i am actually refering to. www.trainweb.org/tubeprune/Tube%20track%20in%20station.htm
If the outside current rail was the same profile as a running rail i am now thinking there wouldn't be enough space beneath it to fit the insulator to maintain the correct surface height and distance from the tunnel sides. Also the cross-section being square may have the same current carrying capacity as a normal rail whilst being smaller in size.
Tell me i haven't just answered my own question.

[Colin]

The physical size of the rail is only really relevant in so far as the size of the collector shoe is concerned, and maintaining it's contact. The actual make up of the rails are very different; running rails are pure steel, where as current rails are either steel or aluminum and contain lots of copper 'bits' to assist the conductivity.

I don't believe the proximity of the tunnel walls has any bearing on current rail size's or positioning - at least not in the way you think.

[towerman]

Don't know if it's still the case,but the Grange Hill end of 63 & 64 roads in Hainault Depot had square type current rails.

[Deleted]

parsons green sidings also has the older type traction rails on i think 23 and 24 road

[mandgc]

Second hand running and current rails are, presumably, considered good enough to re-use on little used, low speed sidings.

[Deleted]

Thanks Guy's.
I found a really interesting website. Although designed for 4mm scale modellers, there's some really good information there. I'm just about to go off to and have a long read.
homepage.ntlworld.com/russelliott/3rd-4th.html
Darren

[russe]

Darren - your deductions are correct: the proximity of the sides of a tube tunnel was and is a significant factor in the choice and use of rectangular section conductor rail for tube applications. The use of flat-bottom subsurface conductor rail section would give problems both in respect of height and footwidth if used in most standard 12' diameter tube tunnels. The diameter of the tunnel for a tube station is of course much larger, but, essentially, the same electrical clearance and dimensional restrictions still apply in most cases.

Rectangular section conductor rail is not as physically strong either vertically or laterally as flat-bottom rail, and requires a different type of cradle between insulator and the rail. These strength and ease of construction issues are why tube lines change to and adopt flat-bottom conductor rail in surface areas. As others have noted, bullhead rail is still to be found, as conductor rail, in subsurface sidings - Acton Town is a good place to spot these.

The current-carrying capacity of 130lb/yard rectangular section is marginally less than that of modern 150lb/yard flat-bottom section, but is more than that of lighter section flat-bottom conductor rails (typically in the region of 100lb/yard), such lighter flat-bottom sections being used in very early years of some subsurface deployment.

Hope you enjoyed my webpage - I hope to add a couple of diagrams when time permits to show tube tunnel cross-sections to illustrate some of the above points.

Russ

[Deleted]

Thanks Russ,
I had no idea that was your website. Excellent, very detailed and informative and lots of great pics. I am in the electrical industry myself which prompted my question in the matter in the first place. Keep up the good work.
Darren.